Reciprocating piston tri-lobed cam engines are disclosed in the following patents:
U.S. Pat. Nos.:
1,765,237; 1,792,062, 1,810,688 2,124,604; 4,697,552
In each of the foregoing patents a pair of diametrically opposed pistons are provided which are coupled together in push-pull relationship by an inextensible link. Each piston has a cam-follower, the link serving to maintain the cam-followers in contact with the cam at all positions of rotation thereof. The coupling together of the pistons in this manner necessitates the shaping of the tri-lobed cam such that the dimension between diametrically opposed portions is substantially constant. Generally speaking, such shaping includes a flattening of the lobes of the cam and the formation of a concavity between adjacent pairs of lobes. These engines have a relatively large angular interval over which they are not self-starting when operated using an externally generated source of pressurized gas, for example when operated as external combustion engines, steam engines and compressed air engines.
In U.S. Pat. No. 1,203,855 there is disclosed a tri-lobed cam engine wherein the pistons are not connected together, whereby they are free-floating. The cam of this engine is asymmetrically shaped, whereby the engine would be suited for operation in one direction only. Moreover, the interaction between the cam-followers and the cam would generate a severe reactive force which urges the piston into contact with the wall of the cylinder in which it reciprocates, promoting a rapid wear.
For certain purposes it may be preferred that the cam be asymmetrical, while retaining the self-starting operation of the engine when operated as an external combustion motor or the like.
In the aforementioned patent application there is disclosed improvements to tri-lobed cam engines which overcome at least in part the above mentioned disadvantages. Such improved engines may be self-starting when operated as external combustion motors, and utilize free floating pistons with bearings to reduce the inter-reactive forces between the piston and cylinder wall, and which may be operated in either forward or reverse direction. In addition, a simple modular design of such improved engines permits the number of cylinders to be easily varied, or the cylinders removed or replaced, with four cylinder and eight cylinder engine units being disclosed.
More particularly, the improved engine described in the above mentioned patent application, comprises a housing with a shaft and tri-lobed cam, and four free-floating piston means disposed on the housing in equi-spaced relationship. Each piston means includes a cylinder and a free floating piston for reciprocal movement within the cylinder and a cam-follower associated with each piston. The cam-follower has associated therewith a guide bearing means and the housing has a track means along which the guide beating means is movable. The guide bearing means serves to reduce cylinder-piston wear by transmitting to the track means reactive forces generated in the cam-follower by the cam, which would otherwise urge the piston into contact with its cylinder.
As a preferred feature, the guide bearing means includes a pair of guide bearings disposed on axially opposed sides of the cam follower, the axial direction of the engine being considered to be that of the engine shaft. Also preferably, the guide bearing means and the cam follower are rotatable and suitably have a collinear axis of rotation.
With the reduction of piston-cylinder interaction and with the rolling motion of the cam follower and associated guide bearing means, the engine is particularly adapted for use as a high torque, essentially oil free air motor for use in the food processing trades.
The four piston means of the engine unit are arranged at ninety degree intervals, with the cylindrical axes of the cylinders intersecting at the axis of the engine shaft, so as to provide a symmetry and reversibility of direction of the engine.
Where eight cylinders are provided in a unit, the cylinders are disposed at forty five degree intervals.
It will be understood that engine units may be coupled together in side by side relationship to form engines having any multiple of four cylinders.